Electronic circuit with reverberation effect and improved output controllability

ABSTRACT

An electronic circuit for adding the effects of reverberation to a high impedance signal produced from an external audio source such as a guitar pickup or a high impedance microphone. The electronic circuit comprises a reverberation effects circuit having pre-amplifier/driver and recovery amplifier sections and a spring reverberation device coupled thereinbetween and a reverberation effects bypass at the circuit&#39;s input, prior to switchably passing the audio signal into an input of the pre-amplifier/driver section which comprises a low impedance, high current output for input into the spring reverberation device having an output for passing a low impedance signal to the recovery amplifier section, which suitably serves in increasing the impedance of the signal to a predetermined level acceptable for input into an external sound device such as an amplifier having channel inputs and audio control capabilities, and a power supply circuit having means for switching between a dc voltage source and an ac voltage source and supplying ±9 volts to integrated circuits (ICs) included in the pre-amplifier/driver and recovery amplifier sections of the reverberation effects circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of my priorapplication U.S. Ser. No. 10/757,833, filed Jan. 14, 2004, entitled“Electronic Circuit with Reverberation Effect and Improved OutputControllability, the disclosures of which, including all attacheddocuments, are incorporated herein by reference in their entirety forall purposes.

FIELD OF THE INVENTION

The present invention relates in general to an electronic circuit foraccepting a high impedance audio signal and adding spring reverberationeffect thereto while maintaining an acceptable impedance range for inputinto an external sound device such as a guitar amplifier, pedal effectsdevice or any other instrument level device.

BACKGROUND OF THE INVENTION

Reverberation is the collection of reflected, discrete sounds or echoesgenerated from surfaces in an enclosure like an auditorium. Musicians,audiophiles and the like strive to add reverberating effects inrecordings and live performances to place a sound within the context ofits space or create new sounds of their own, not necessarily relating toany existing physical space. The prior art currently offers electronicreverberation units or techniques which can simulate a number ofacoustic environments and give control over the amount of reverberationadded to an audio signal. One notable technique is convolution, whichinvolves recording the ambience of a room under controlled conditionsand superimposing the resultant recording onto a sound recordedelsewhere. A less costly and more practical approach of reverberation isthe spring reverb, which is often electronically made part of some soundmixing boards, pedal effect devices, pre-amplifiers, and guitaramplifiers. Inherent in these devices is the lack of varied means forcontrolling or manipulating the reverberation effect besides that of thereverberation device such as through the use of an external amplifier oran effects pedal device for improved replication of an acoustical spaceor increased production of a new sound effect. In most designconfigurations, the reverberation device, whether it is analog ordigitally based, comprises means for accepting an audio signal from amusical source and combining the signal with effects of reverberationfollowed by amplification collectively occurring internally therewithin.The extent to which reverberation is added to the audio signal andmanipulated is primarily controlled at the interface of the of springreverberation device rather than through other available sound enhancingmeans. Consequently, limitations are immediately placed upon themusician in attempting to simulate a particular acoustical space, createentirely new sound effects, or replicate sounds of the past,specifically the warm “vintage sound” so often associated with thepreferred tube driven spring reverberation devices of the 50's and 60's.

In accordance with the present invention, applicant has appreciablydevised an electronic circuit which provides for varied alteration ormanipulation of the reverberation effect besides that of thereverberation device to offer the musician or audiophile versatile meansto enhance replication of an acoustical space or create entirely newsounds during a recording session or live performance.

BRIEF SUMMARY OF THE INVENTION

In order to overcome the numerous drawbacks apparent in the prior art, aelectronic circuit incorporating reverberation has been devised for usewith an external sound device such as a guitar amplifier, pedal effectsdevice or other instrument level devices often employed in recordingsand live performances.

It is thus an object of the present invention to provide a low cost,non-complicated device which may be reliably used in enhancing thereverberation effect to more accurately simulate a preexistingacoustical environment substantially by means other than those generallymade available at the reverberation device.

It is another object of the present invention to provide such anelectronic circuit incorporating reverberation which affords versatilityto the musician to permit production of sounds not necessarilyassociated with or related to a known acoustical space.

It is another object of the present invention to provide such anelectronic circuit incorporating reverberation which possesses audiosignal outputs comprising an impedance level substantially equivalent toan audio signal produced by a musical source such as an electric guitarpickup, harmonica microphone, or other high impedance instrument output.

It is another object of the present invention to provide such anelectronic circuit incorporating reverberation which is portable forconvenient transport to recording sessions and live performances andcompatible with most vintage amplifiers lacking in most cases means foradding the effect of reverberation such as a tube driven amplifier.

It is another object of the present invention to provide such anelectronic circuit incorporating reverberation which comprises an audiosignal bypass of suitable impedance for input into a two channelamplifier to increase the effectiveness of the reverberation effect ornewly created sounds.

It is yet another object of the present invention to provide such anelectronic circuit incorporating reverberation which accomplishes theforegoing and other objects and advantages and which is economical,durable, and fully effective in performing its intended functionswithout undue retrofitting of existing sound equipment, includingwithout limitation, amplifiers, effects pedal device, sound mixingboards, etc.

In accordance with the present invention, an electronic circuitincorporating reverberation has been devised for use with an externalsound device such as an amplifier or an effects pedal device, theelectronic circuit comprising in combination a reverberation effectscircuit having a pre-amplifier/driver and recovery amplifier sectionsand a spring reverberation device coupled thereinbetween, thepre-amplifier/driver section having an input jack for receivingtherethrough a high impedance signal produced from an external audiosource and a low impedance, high current output for input into thespring reverberation device having an output for passing a low impedancesignal to the recovery amplifier section, which suitably increases theimpedance of the signal to a predetermined level acceptable for inputinto the external sound device, and a power supply circuit having meansfor switching between a dc voltage source and an ac voltage source andsupplying +9 volts to integrated circuits (ICs) included in thepre-amplifier/driver and recovery amplifier sections of thereverberation effects circuit.

Other objects, features, and advantages of the present invention willbecome apparent in the following detailed description of the preferredembodiments thereof when read in conjunction with the accompanyingdrawings in which like reference numerals depict the same parts in thevarious views.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A preferred embodiment of the present invention will now be described byway of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a reverberation effectscircuit of the preferred embodiment of the present invention;

FIG. 2 is a schematic diagram illustrating a power supply circuit of thepreferred embodiment of the present invention;

FIG. 3 is a block diagram depicting signal flow through a preferredembodiment of the present invention;

FIG. 4 is a block diagram illustrating the preferred embodiment of thepresent invention in a two-channel configuration; and

FIG. 5 is a block diagram illustrating the preferred embodiment of thepresent invention in a one-channel configuration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of being embodied in many differentforms, the preferred embodiment of the invention is illustrated in theaccompanying drawings and described in detail hereinafter with theunderstanding that the present disclosure is to be considered toexemplify the principles of the present invention and is not intended tolimit the invention to the embodiments illustrated and presented herein.The present invention has particular utility as a device for adding andenhancing the effects of reverberation while maintaining an impedancelevel made suitable for application with external sound devices such asa guitar amplifier, an effects pedal device, or other instrument leveldevice.

Referring to FIG. 1, there is shown generally at 10 a schematic diagramof the reverberation effects circuit of the present invention driven bya power supply circuit switchable between a conventional high current,low impedance source and a low dc voltage source consisting of a pair of9 volt batteries as collectively represented in FIG. 2. A relay RL1operatively switches the power source from dc to ac particularlyoccurring upon an outside power source of 120 vac/60 Hz being coupled toa transformer T1, notwithstanding the presence of the low dc voltsource. In this regard, the power supply is responsive to voltage from aline connection, through transformer and a mono phone jack J1, andincludes a conventional rectifying circuit as established by a pair ofdiode/capacitor groupings of D1, C1 and D2, C2, each grouping of whichserving as an appropriate filter for converting an ac voltage source todc, which is needed to operate a plurality of integrated circuits (ICs)integrally made part of the amplifying sections of the reverberationeffects circuit. Given that each of the ICs operate at a specifiedvoltage as determined by the manufacturer, the power supply circuitfurther comprises a pair of adjustable voltage regulators IC1, IC2,which, acting in concert with a pair of resister groups R1, R2 and R3,R4, respectively, suitably establishes bipolar outputs of 9 volts atapproximately 125 milliamps. To further serve in filtering the signaland mitigating the presence of voltage spikes prior to being fed intoand coupled to relay RL1, voltage line outputs from IC1 and IC2 eachcomprise a diode/capacitor grouping of D3, C3 and D4, C4, respectively.As shown in FIG. 2, RL1's normally closed contacts are coupled to 9 voltbatteries while the normally open contacts are coupled to the bipolaroutputs from IC1 and IC2. Upon coupling the external power supply of 120vac/60 Hz to T1, RL1 energizes and closes the NO contacts whicheffectively disconnect the 9 volt batteries from the reverberationeffects circuit, more specifically the ICs. Conversely, when T 1 isdisconnected from the 120 vac/60 Hz source, the ICs become operationalfrom the 9 volt batteries via J4 and J5 phone jacks. Only upon theinstance of J4 and J5 being coupled to an external phone plug will thebatteries supply power to the reverberation effects circuit, otherwisethe batteries will not have a return path to ground. This arrangementeffectively serves as a visual safeguard against inadvertently leavingthe circuit powered up strictly under battery power.

Referring now to FIG. 1, the reverberation effects circuit furthercomprises a pre-amplifier/driver circuit 12 for conditioning the audiosignal input prior to being fed into a reverb pan RP, particularly interms of setting the correct impedance at the input side of the RP andestablishing ample current to drive the transducers inherently made partof the RP and a recovery amplifier section 14 for increasing the signalimpedance to a predetermined level prior to being passed to an externalsound device. First and second operational amplifiers IC3 a and IC3 bform the pre-amplifier/driver section of the reverberation effectscircuit which primarily amplifies and controls the audio input signalprior to being fed into the input transducer of RP. Audio input signalis initially applied at input connection J2 and branches into twodiscrete signal pathways, one of which extending from the input to anopen phone jack J4, which substantially serves as a reverberationeffects bypass, and a second pathway extending to a switch SW1. In aclosed state, SW1 passes the audio input signal to the non-invertinginput of IC3 b via R6, which pads the audio signal prior to reaching IC3b to prevent possible overloading into IC3 b which may lead toundesirable distortion and noise. A path to ground via R7 prior topassing the signal to the inverting input of IC3 b substantially servesin keeping an audio signal feed of a guitar or other high impedancesource from being loaded into IC3 b. A path to ground from J2effectively serves in protecting signal from noise caused by thepresence of RFI and EMI. Amplifier IC3 b is operated with a negativefeedback comprising a 50K linear potentiometer VR1 having variableresistive capacity to appropriately adjust the gain at the output pathof IC3, specifically in light of the resistive value of R5 beingselectively coupled to the inverting input of IC3 b. In an operativestate, the feedback voltage is dropped by the varying resistive valuesof VR1 and shunted to ground via R5 and J2, collectively establishing anoutput at IC3 b having a low impedance, low noise response and a gainfactor approaching upwards of 23. The output pathway of IC3 b is coupledto the non-inverting input of IC3 a via a pair polarized capacitors C5,C6, which appropriately serve to block the passing of any dc signal intoIC3 a while permitting the passage of the audio signal for eventualinput into RP. Powering of the dual op-amps IC3 a, IC3 b is principallyestablished by the ±9 volt rails from the power supply circuit notedabove. A path to ground for the negative and positive voltage leads eachincorporate a capacitor C9 and C10, respectively, to suitably filter andestablish steady line voltage to IC3 a and IC3 b. To moderately increasethe gain at low frequencies at IC3 a and minimize the gain at highfrequencies to the extent of enhancing the effects of reverberation, theinverting input of IC3 a is supplied with a resistor/capacitorarrangement R8, C7 shunted to ground. The presence of C7 at the groundpath of the inverting input effectively serves in filtering or rollingoff a predetermined amount of high frequencies and limits the extent ofhigh frequency feedback at the inverting input in the event VR1 is setat a high resistive level. Output from IC3 a is coupled to the inputside of RP and comprises a negative feedback loop having also aresistor/capacitor arrangement R9, C8, which collectively stabilizes thefeedback loop and restores phase margin to the IC3 a networkedcircuitry. A path to ground from the input side of RP is provided andterminates at the feedback loop of IC3 a prior to and after theresistor/capacitor arrangements of R8, C7 and R9, C8, respectively. Inpreferred applications, RP comprises a spring reverberation device ofthe type having a 3-spring configuration operable at an input impedanceof 800 ohms and an output impedance of 2575 ohms, as notablymanufactured by Accutronics as Model No. 8EB2C1B. It is noted herein,however, that standalone reverberation devices manufactured by companiesother than Accutronics may be suitable for this application providingthey meet the above specifications and cooperate with and operate withinthe limitations of the ICs integrally made part of the amplifier/driverand recovery amplifier sections of the reverberation effects circuit.

Referring now to the recovery amplifier section 14 of the reverberationeffects circuit 10 in FIG. 1, a reverberated output signal from RP iscoupled to the inverting input of IC4 via a resistor/capacitorarrangement R10, C11, whereas C11 primarily serves in the capacity ofrolling off the low frequency gain of the circuit prior to reaching IC4.A path to ground is provided for the non-inverting input and theinverting input via capacitor C12 to mitigate high frequency feedback atthe output of IC4. Like IC3 b, IC4 comprises an output signalincorporating a negative feedback loop but comprises a 100K linearpotentiometer VR2 to suitably establish a gain factor of approximately 5at the output of IC4, as cooperatively established by the resistivecapacity of R10. The higher resistive capacity of VR2 in light of thevalue for VR1 suitably allows adjustment of the gain to correspond morefully with the gain outputs at VR1 of the pre-amplifier/driver circuitregardless of the level of reverberation added to the audio signal. Inother words, the varying resistive capacities of VR1 and VR2 and theupward resistive limit of VR2 collectively serve in retaining thedesired amount of reverberation, as principally controlled by the dwellcontrol at VR1, and amplifying the reverberated signal to apredetermined gain for a more predominant positioning in the soundstage.Powering of IC4 is principally established by the ±9 volt rails from thepower supply circuit noted above. Each of the ±9 volt rails receive adiode D6, D5 for filtering applied voltage and ensuring correct polaritypassing into IC4. A path to ground for the negative and positive voltagerails each incorporate a capacitor C13 and C14, respectively, tosuitably filter and establish steady line voltage to IC4. Output signalfrom IC4 is directed to an output phone jack J5 via capacitor C15, whichsuitably serves in filtering voltage spikes to ensure steady linevoltage to an external sound enhancing device such as a guitar amplifieror effects pedal device. Coupled in between C15 and J5 is path to groundpassing through resistor R11 to reinforce the impedance strength of thesignal exiting IC4 and ensure impedance matching with that of theexternal sound enhancing device. An input jack J3 comprising a switchSW2 provides means for clamping a signal to ground, which is useful incontrolling sound effects at the external sound device intermittentlyduring a performance or recording session. A schematic of signal flowthrough the reverberation effects circuit is provided in FIG. 3.

Table 1 attached hereto lists the values of the circuit componentsdescribed herein. However, it is to be understood that the invention isnot limited to the precise circuit values or even the specificembodiment described above, and no limitation with respect to thespecific apparatus illustrated herein is intended or should be inferred.It can be appreciated that numerous variations and modifications may beeffected without departing from the true spirit and scope of the novelconcept of the invention. It is of course intended to cover by theappended claims all such modifications as fall within the scope of theclaims. TABLE 1 C1, C2 2200 uf/16 V electrolytic capacitor C3, C4 1 of35 V Tantalum capacitor IC1 LM317 Adj. +9 volt regulator IC2 LM337 Adj.−9 volt regulator R1, R4 180 ohm ¼ watt metal film resistor R2, R3 1.15k¼ watt metal film resistor D1-D4 1 n4001 diode RL1 24 volt dpdt diprelay SW1, SW2 spst Carling footswitch R5, R9 2.2k ¼ watt metal filmresistor R6 1k ¼ watt metal film resistor R7 1 M ¼ watt metal filmresistor R8 47 ohm ¼ watt metal film resistor R10 22K ¼ watt metal filmresistor R11 10K ¼ watt metal film resistor D5, D6 In914 diode C5, C6 47uf/50 v electrolytic capacitor C7 100 uf/50 v electrolytic capacitor C8.01 of/100 v polyester film capacitor C9, C10 .1 of/50 v polyester filmcapacitor C11 .22 uf/50 v polyester film capacitor C12 270 pf ceramicdisc capacitor C13, C14, C15 100 uf/25 v electrolytic capacitor VR1 50Klinear potentiometer VR2 100K linear potentiometer IC3a, IC3b 5532 DualOperational amplifier IC4 741 Single Operational amplifier J1 3.5 mmmono phone jack J2 ¼″ mono closed phone jack J3 ¼″ mono open phone jackJ4, J5 ¼″ stereo open phone jack T1 120 vac primary/12 vac secondary,rated @ 500 mA w/3.5 mm phone plug B1, B2 9 volt Alkaline Battery RPAccutronics ® Model 8EB2C1B

In operation, a musical instrument such as a guitar or a harmonicamicrophone having an output line feed is coupled to J2. Activating SW1simultaneously provides passage of the audio signal to the reverberationeffects circuit for addition of reverb and directly into the externalsound enhancing device such as a guitar amplifier, effectively bypassingthe addition of reverberation. In a two-channel configuration as shownin FIG. 4, which comprises dedicated controls for both channels at theamplifier, the guitar's direct output is coupled to one channel and theaudio signal exiting the reverberation effects circuit via J5 is coupledto the second channel. Using this configuration, the dwell and outputlevel controls referred herein as VR1 and VR2, respectfully, togetherwith the volume and tonal controls of the amplifier collectively serveas further means for controlling the effects for reverberation for amore accurate simulation of an acoustical space or creation of a newsound effect. In a one-channel configuration as shown in FIG. 5, whichcomprises two instrument inputs at the amplifier, the effects ofreverberation is balanced with the guitar's direct sound through use ofVR1 and VR2 at the reverberation effects circuit. Regardless of theconfiguration of connectivity, the reverberation effects circuit outputsJ4 and J5 are preferably fitted with shielded cable of the guitar ormicrophone type utilizing a ¼″ phone plug. Final operational setupinvolves configuring the power supply circuit to accept either acvoltage from an outside 120 vac/60 Hz power source or dc voltagesupplied by a pair of 9 volt batteries. In a configuration utilizing acpower, T1 is coupled to J1 with line inputs of T1 being coupled to anexternal 120 vac/60 Hz power supply. In a configuration utilizing dcpower, the reverberation effects circuit is operational upon installinga pair of 9 volts batteries, connecting cables of suitable type to J4and J5, and disconnecting T1 from the power supply circuit. Followingthe application of power to the reverberation effects circuit and guitaramplifier, the guitar amplifier is activated while the volume controlsof the amplifier are adjusted accordingly for each channel. VR1 (dwell)suitably controls the extent to which reverberation is added to theaudio signal, while VR2 controls the level of the reverb signal. Toremove the effects of reverberation from the amplified signal, depressSW 1. To re-activate the effects of reverberation, depress SW 1 oneadditional time.

To create distinct sounds for application during recordings and liveperformances, the reverberation effects circuit outputs J4 and J5 can becoupled in a particular manner with an external amplifier havinginstrument inputs for each channel and audio control capabilities (e.g.,base, treble and volume). For instance, the reverberation effectscircuit output at J5 can be coupled to a tremolo channel of the externalamplifier, while the direct signal output at J4 can be coupled to anormal channel of the amplifier to create a realistic echo effect byutilizing the frequency and depth controls of the external amplifier andVR1 and VR2 at the reverberation effects circuit. In an another example,the depth of the reverberation effect can be effectively increased bypassing the signal from an external audio source (e.g., guitar) into anexternal reverberation amplifier via J4 and coupling J5 to the normalchannel of an external amplifier for simultaneous reverberation effectfrom two sources. Although the present invention is described by way ofexample to cooperate and function with an external amplifier, otherapplications may be utilized to facilitate the addition of reverberationto an audio signal given that the input at J2 can accept a highimpedance source and that the outputs at J4 and J5 can pass along a highimpedance signal matching most other instrument devices, includingwithout limitation modern console pre-amplifiers with direct injection(DI) for balancing line level outputs and pedal type effect units. Inthis regard, instrument devices of these types may be coupled to J2 orJ5 without adversely impacting the reverberation effects circuit.

While there has been shown and described a particular embodiment of theinvention, it will be obvious to those skilled in the art that variouschanges and alterations can be made therein without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and alterations as fall within the true spirit andscope of the invention.

1. An electronic circuit for adding reverberation effects to an audiosignal produced from an external high impedance source and passing thereverberated audio signal at a predetermined impedance for input into anexternal sound device, said electronic circuit comprising, incombination: a pre-amplifier/driver circuit having a first operationalamplifier coupled to a second operational amplifier, each operationalamplifier having inverting and non-inverting inputs and an output, eachof said outputs comprising a negative feedback loop coupled to saidinverting input and shunted to ground for setting a predetermined gainat each of said outputs, said non-inverting input of first operationalamplifier having an input jack for receiving therethrough the audiosignal produced from the external high impedance source; a springreverberation device having an input coupled to said output of secondoperational amplifier and an output for passage of a reverberated, lowimpedance signal; a recovery amplifier circuit comprising a singleoperational amplifier having an inverting input for receiving thereverberated, low impedance signal and a non-inverting input shunted toground and an output comprising a negative feedback loop coupled to saidinverting input for setting the reverberated, low impedance signal at apredetermined gain and impedance for input into the external sounddevice; and a power supply circuit having means for switching between adc voltage source and an ac voltage source most suitable for poweringsaid first and second and single operational amplifiers.
 2. Anelectronic circuit as set forth in claim 1, wherein said input jackcomprises a reverberation effects bypass for maintaining the integrityand impedance of the audio signal produced by the external highimpedance source for direct input into the external sound device.
 3. Anelectronic circuit as set forth in claim 1, wherein said non-invertinginput of first operational amplifier comprises a switch for controllingthe audio signal input and a path to ground comprising resistivecapacity for maintaining an impedance level into said first operationalamplifier and keeping the external high impedance source from beingloaded.
 4. An electronic circuit as set forth in claim 1, wherein saidnegative feedback loop of first operational amplifier comprises a 50Klinear potentiometer having variable resistive capacity to variablyadjust gain of the audio signal and establish low impedance at saidoutput of first operational amplifier.
 5. An electronic circuit as setforth in claim 1, wherein said negative feedback loop of singleoperational amplifier comprises a 100K linear potentiometer havingvariable resistive capacity to variably adjust the audio signal's gainand impedance at said output of single operational amplifier prior tobeing fed into the external sound device.
 6. An electronic circuit asset forth in claim 1, wherein said output of first operational amplifieris coupled to said non-inverting input of second operational amplifierhaving a filter coupled therebefore for blocking passage of dc signalswhile allowing passage of the audio signal into said second operationalamplifier, said negative feedback loop of second operational amplifiercomprising a resistor/capacitor arrangement for stabilizing saidfeedback loop and restoring phase margin to said second operationalamplifier.
 7. An electronic circuit as set forth in claim 1, whereinsaid power supply circuit comprises a transformer for lowering voltagefrom an outside voltage source from 120 volts ac to 12 volts ac prior topassing into a rectifying portion for converting the voltage source fromac to dc, said power supply further comprising a pair of adjustablevoltage regulators operably establishing power outputs of ±9 volts forinput into a relay having switching capabilities with a pair of 9 voltbatteries coupled thereto and an output coupled to said first and secondand single operational amplifiers.
 8. An electronic circuit as set forthin claim 1, wherein said spring reverberation device comprises a3-spring configuration operable at an input impedance of 800 ohms and anoutput impedance of 2575 ohms.
 9. An electronic circuit as set forth inclaim 1, wherein said recovery amplifier circuit comprises an auxiliaryjack fitted with a switch for clamping a signal to ground tointermittently control the external sound device.
 10. An electroniccircuit as set forth in claim 1, wherein said inverting input of secondoperational amplifier comprises a resistor/capacitor arrangementsubstantially serving as means for filtering a predetermined amount ofhigh frequencies and limiting the extent of high frequency feedback atsaid inverting input of second operational amplifier particularlyoccurring upon said 50K linear potentiometer being set at a highresistive level.
 11. A method for adding reverberation effects to anaudio signal produced from an external high impedance device and passingthe reverberated audio signal to an external sound device at apredetermined impedance, said method comprising the steps of: sendingthe audio signal into an non-inverting input of a first operationalamplifier having an inverting input shunted to ground and an outputcomprising a negative feedback loop coupled to said inverting input forsetting said output at a predetermined gain and impedance prior to beingpassed into a non-inverting input of a second operational amplifierhaving an inverting input shunted to ground and a low impedance, highcurrent output for input into a spring reverberation device having anoutput for passing therethrough a reverberated, low impedance signal,said negative feedback loop of first operational amplifier comprising a50K linear potentiometer having variable resistive capacity to variablyadjust gain of the audio signal and establish low impedance at saidoutput of first operational amplifier; passing the reverberated, lowimpedance signal into an inverting input of a single operationalamplifier having a non-inverting input shunted to ground and an outputhaving a negative feedback loop coupled to said inverting input, saidnegative feedback loop of single operational amplifier comprising a 100Klinear potentiometer having variable resistive capacity to variablyadjust the audio signal's gain and establish a low impedance at saidoutput of single operational amplifier prior to being fed into theexternal sound device; and supplying power from an external source to apower supply circuit having means for switching between a dc voltagesource and an ac voltage source most suitable for powering said firstand second and single operational amplifiers.
 12. A method as set forthin claim 11, wherein said negative feedback loop of second operationalamplifier comprises a resistor/capacitor arrangement for stabilizingsaid feedback loop and restoring phase margin to said second operationalamplifier.
 13. A method as set forth in claim 11, wherein said invertinginput of second operational amplifier comprises a resistor/capacitorarrangement substantially serving as means for filtering a predeterminedamount of high frequencies and limiting the extent of high frequencyfeedback at said inverting input of second operational amplifierparticularly occurring upon said 50K linear potentiometer being set at ahigh resistive level.
 14. A method as set forth in claim 11, furthercomprising the step of coupling a switch at said non-inverting input offirst operational amplifier for controlling the addition ofreverberation to the audio signal and a reverberation effects bypassprior to said switch for maintaining the integrity and impedance of theaudio signal for direct input into the external sound device.
 15. Amethod as set forth in claim 11, wherein said spring reverberationdevice comprises a 3-spring configuration operable at an input impedanceof 800 ohms and an output impedance of 2575 ohms.
 16. An electroniccircuit for adding reverberation effects to an audio signal producedfrom an external high impedance source and passing the reverberatedaudio signal at a predetermined impedance for input into an externalsound device, said electronic circuit comprising, in combination: afirst operational amplifier having inverting and non-inverting inputsand an output comprising a negative feedback loop coupled to saidinverting input and shunted to ground, said negative feedback loop offirst operational amplifier comprising a 50K linear potentiometer havingvariable resistive capacity to variably adjust the audio signal's gainand impedance at said output of first operational amplifier, saidnon-inverting input of first operational amplifier having an input jackfor receiving therethrough the audio signal produced from the externalhigh impedance source, said input jack comprising a reverberationeffects bypass for maintaining the integrity and impedance of the audiosignal produced by the external high impedance source for direct inputinto the external sound device; a second operational amplifier havinginverting and non-inverting inputs and an output comprising a negativefeedback loop coupled to said inverting input and shunted to ground,said output of first operational amplifier being coupled to saidnon-inverting input of second operational amplifier having a filtercoupled therebefore for blocking passage of dc signals while allowingpassage of the audio signal into said second operational amplifier, saidnegative feedback loop of second operational amplifier comprising aresistor/capacitor arrangement for stabilizing said feedback loop andrestoring phase margin to said second operational amplifier; a springreverberation device having an input for accepting a low impedance, highcurrent signal from said output of second operational amplifier and anoutput for passing therethrough a reverberated, low impedance signal; asingle operational amplifier having an inverting input for receiving thereverberated, low impedance signal and a non-inverting input shunted toground and an output comprising a negative feedback loop coupled to saidinverting input, said negative feedback loop of single operationalamplifier comprising a 100K linear potentiometer having variableresistive capacity to variably adjust the audio signal's gain andestablish a low impedance at said output of single operational amplifierprior to being fed into the external sound device; and a power supplycircuit having a transformer for lowering voltage from an outsidevoltage source from 120 volts ac to 12 volts ac prior to passing into arectifying portion for converting the voltage source from ac to dc, saidpower supply circuit comprising a pair of adjustable voltage regulatorsoperably establishing power outputs of ±9 volts for input into a relayhaving switching capabilities with a pair of 9 volt batteries coupledthereto and an output coupled to said first and second and singleoperational amplifiers.
 17. An electronic circuit as set forth in claim16, wherein said spring reverberation device comprises a 3-springconfiguration operable at an input impedance of 800 ohms and an outputimpedance of 2575 ohms
 18. An electronic circuit as set forth in claim16, wherein said output of reverberation device comprises aresistor/capacitor arrangement substantially serving as means forrolling off high frequency gain from the reverberated, low impedancesignal prior to being passed into said inverting input of singleoperational amplifier.
 19. An electronic circuit as set forth in claim16, wherein said output from said single operational amplifier comprisesa capacitor to filter voltage spikes prior to passing the audio signalto the external sound device and a path to ground having resistivecapacity to reinforce and increase the impedance of the audio signalfrom said output of single operational amplifier to substantiallycorrespond to the impedance of the external sound device.
 20. Anelectronic circuit as set forth in claim 16, wherein said non-invertinginput of first operational amplifier comprises a switch for controllingthe audio signal input and a path to ground comprising resistivecapacity for maintaining a predetermined impedance into said firstoperational amplifier and keeping the external high impedance sourcefrom being loaded.